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Illuminating the Path Forward for Seattle's Pioneer Square Prisms

The glass prisms found throughout Seattle's Pioneer Square were built to provide natural light to the subterranean passages constructed below after the Great Fire of 1889.

The future is bright for the glittering purple glass prisms of the Pioneer Square neighborhood in Seattle. Since the National Trust partnered with the Alliance for Pioneer Square in May of 2017 as part of The Cities Project by Heineken, over $40,000 were raised for the prisms’ preservation. However, many of the square’s prism panels are still in need of attention. And since the responsibility for their maintenance falls to each individual property owner—the majority of whom lack familiarity with them—empowering the prisms’ stewards to preserve them properly remained a challenge.

But that’s all in the past with the Alliance for Pioneer Square’s recently completed Pioneer Square Prism Glass Design Manual, the first document to guide property owners, developers, and engineers alike through the process of repairing these city gems. The handy booklet contains graphics and flowcharts that help demonstrate how the prisms were constructed, which stretches of sidewalk are most in need of attention, and what steps need to be taken to ensure the prisms’ longevity.

"From a practical standpoint, sidewalk repairs can be both costly and complicated for building owners to undertake," says Lisa Howard, executive director of the Alliance. "We developed the guide to give owners a road map to complete repairs more easily, while also meeting all the various permitting and historic preservation requirements in our district."

For example, one section of the manual discusses the two methods used to construct the prism glass panels back in the 19th century. Some of them were built out of cast iron, with the prisms grouted to the panels. More common in Pioneer Square are precast concrete panels with reinforcing bars, where the prisms are protected by waterproof caulking or grout. The methods are displayed in easily-digestible diagrams, allowing property owners to visualize the components of their sidewalk adornments.

“The prism glass sidewalks are a unique feature of Pioneer Square," Howard says. "They contribute to the neighborhood’s historic character and give visitors a look into the storied history of where Seattle began."

photo by:
Lindsey Miller

Replacement prisms must be purple to maintain aesthetic consistency in the neighborhood.

photo by:
Lindsey Miller

A damaged prism in a precast concrete panel containing several other paved-over prisms.

photo by:
Lindsey Miller

Many prisms have become discolored over time due to chemical interaction between the glass and pavements.

photo by:
Lindsey Miller

The prisms can be enjoyed by people and pups alike.

Nicholas Som is an editorial assistant at Preservation magazine. He enjoys museums of all kinds, Philadelphia sports, and tracking down great restaurants.